Fix bolt on OpenBSD.

OpenBSD does not include a UBC kernel and writes must be synchronized
with the msync(2) syscall.  In addition, the NoSync field of the DB
struct should be ignored on OpenBSD, since unlike other platforms,
missing msyncs will result in data corruption.

Depends on PR #258.

Fixes #257.

bolt_linux.go

@@ -1,13 +1,12 @@
 package bolt
 
 import (
-	"os"
 	"syscall"
 )
 
 var odirect = syscall.O_DIRECT
 
 // fdatasync flushes written data to a file descriptor.
-func fdatasync(f *os.File) error {
+func fdatasync(db *DB) error {
-	return syscall.Fdatasync(int(f.Fd()))
+	return syscall.Fdatasync(int(db.file.Fd()))
 }

bolt_openbsd.go

@@ -0,0 +1,29 @@
+package bolt
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+const (
+	msAsync      = 1 << iota // perform asynchronous writes
+	msSync                   // perform synchronous writes
+	msInvalidate             // invalidate cached data
+)
+
+var odirect int
+
+func msync(db *DB) error {
+	_, _, errno := syscall.Syscall(syscall.SYS_MSYNC, uintptr(unsafe.Pointer(db.data)), uintptr(db.datasz), msInvalidate)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
+
+func fdatasync(db *DB) error {
+	if db.data != nil {
+		return msync(db)
+	}
+	return db.file.Sync()
+}

bolt_windows.go

@@ -11,8 +11,8 @@ import (
 var odirect int
 
 // fdatasync flushes written data to a file descriptor.
-func fdatasync(f *os.File) error {
+func fdatasync(db *DB) error {
-	return f.Sync()
+	return db.file.Sync()
 }
 
 // flock acquires an advisory lock on a file descriptor.

boltsync_unix.go

@@ -1,14 +1,10 @@
-// +build !windows,!plan9,!linux
+// +build !windows,!plan9,!linux,!openbsd
 
 package bolt
 
-import (
-	"os"
-)
-
 var odirect int
 
 // fdatasync flushes written data to a file descriptor.
-func fdatasync(f *os.File) error {
+func fdatasync(db *DB) error {
-	return f.Sync()
+	return db.file.Sync()
 }

db.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"hash/fnv"
 	"os"
+	"runtime"
 	"runtime/debug"
 	"strings"
 	"sync"
@@ -23,6 +24,12 @@ const version = 2
 // Represents a marker value to indicate that a file is a Bolt DB.
 const magic uint32 = 0xED0CDAED
 
+// IgnoreNoSync specifies whether the NoSync field of a DB is ignored when
+// syncing changes to a file.  This is required as some operating systems,
+// such as OpenBSD, do not have a unified buffer cache (UBC) and writes
+// must be synchronzied using the msync(2) syscall.
+const IgnoreNoSync = runtime.GOOS == "openbsd"
+
 // DB represents a collection of buckets persisted to a file on disk.
 // All data access is performed through transactions which can be obtained through the DB.
 // All the functions on DB will return a ErrDatabaseNotOpen if accessed before Open() is called.
@@ -39,6 +46,9 @@ type DB struct {
 	// a system failure or database corruption. Do not set this flag for
 	// normal use.
 	//
+	// If the package global IgnoreNoSync constant is true, this value is
+	// ignored.  See the comment on that constant for more details.
+	//
 	// THIS IS UNSAFE. PLEASE USE WITH CAUTION.
 	NoSync bool
 
@@ -263,7 +273,7 @@ func (db *DB) init() error {
 	if _, err := db.ops.writeAt(buf, 0); err != nil {
 		return err
 	}
-	if err := fdatasync(db.file); err != nil {
+	if err := fdatasync(db); err != nil {
 		return err
 	}
 

tx.go

@@ -425,8 +425,8 @@ func (tx *Tx) write() error {
 		// Update statistics.
 		tx.stats.Write++
 	}
-	if !tx.db.NoSync {
+	if !tx.db.NoSync || IgnoreNoSync {
-		if err := fdatasync(tx.db.file); err != nil {
+		if err := fdatasync(tx.db); err != nil {
 			return err
 		}
 	}
@@ -448,8 +448,8 @@ func (tx *Tx) writeMeta() error {
 	if _, err := tx.db.ops.writeAt(buf, int64(p.id)*int64(tx.db.pageSize)); err != nil {
 		return err
 	}
-	if !tx.db.NoSync {
+	if !tx.db.NoSync || IgnoreNoSync {
-		if err := fdatasync(tx.db.file); err != nil {
+		if err := fdatasync(tx.db); err != nil {
 			return err
 		}
 	}